High flare breakaway guardrail terminal

ABSTRACT

A guardrail system having a standard length-of-need section and a terminal end, the terminal end having a high effective flare rate of at least 5:1 is provided with two independent and cooperating cable anchor systems. One of the cable anchor systems is a side impact releasing mechanism which may include a strut connecting a first and a second breakaway post; a strut anchor release affixed at a first end to a first breakaway post and at a second end to the rail element; a strut with a plug weld anchor release; a strut with a shear bolt anchor release; and a strut with an angled plate anchor release.

This utility application claims priority to co-pending U.S. ProvisionalPatent Application Ser. No. 60/872,856, filed Dec. 5, 2006.

BACKGROUND OF THE INVENTION

The major components of a W-beam type guardrail system include astandard guardrail section and terminals at each end of the standardsection. The standard guardrail section shields errant vehicles fromroadside hazards by containing and redirecting the vehicles on sideimpacts. A guardrail terminal section must safely accommodate errantvehicles for both end-on impacts and side impacts near the terminalends. For side impacts beyond a specified point, which in the art istypically selected to be 12 ft-6 in. from the end of the terminal, theterminal section must also serve the function of containing andredirecting an errant vehicle and not allow it to gate or pass through.This specified point is known in the art as the “beginning oflength-of-need.”

W-beam guardrails use tensile forces developed in the rail element asthe means to contain and redirect errant vehicles during side impacts.The tensile force in the rail element is then transmitted to anchors inthe ground via cables at the ends of both terminals. Thus, the anchorhas to be strong enough to handle the tensile forces. Further, theanchor has to be of a breakaway design for the terminal to functionproperly upon end-on impacts and side impacts near the end of theterminal.

For end-on impacts, existing guardrail terminals may be grouped into twogeneral categories: a) energy absorbing, and b) non-energy absorbing.

Energy absorbing terminals incorporate a mechanism for dissipating theimpact energy to bring an errant vehicle to a controlled and safe stop.Examples of such energy absorbing terminals include: the SequentialKinking Terminal (SKT), Flared Energy Absorbing Terminal (FLEAT), andET-2000. It should be noted that energy absorbing terminals onlydissipate large amounts of impact energy during low-angle end-onimpacts. If a vehicle strikes the end of the terminal at an angle of 15degrees or more, energy absorbing terminals will allow vehicles tosafely pass or “gate” through the guardrail system.

Non-energy absorbing guardrail terminals are designed to allow theerrant vehicle to safely pass or “gate” through the terminal and proceedbehind the guardrail. The gating process does not dissipate much of theimpact energy or slow down the vehicle significantly. The typical gatingmechanism is to flare the end of the terminal away from the tangentsection of the guardrail. Examples of existing non-energy absorbingguardrail terminals include: Breakaway Cable Terminal (BCT), EccentricLoader Terminal (ELT), Modified Eccentric Loader Terminal (MELT),Slotted Rail Terminal (SRT), and the REGENT.

In end-on impacts with non-energy absorbing terminals, the rail elementwould be loaded eccentrically due to the end offset of the terminal fromthe tangent of the standard section. The eccentric loading causes therail element to buckle without imparting excessive decelerations on thevehicle. After the rail element buckles, the vehicle gates through theterminal and proceeds behind the guardrail. Similarly, in side impactsnear the ends of the terminals, the vehicle bends the end of the railelement and then proceeds behind the guardrail.

The High Flare Breakaway Guardrail Terminal of the present invention(herein referred to as the HFT), as described in this disclosure, is anon-energy absorbing or gating terminal. However, it utilizes asignificantly higher effective flare rate of at least 5 to 1, or 4 ft ormore of end offset effected over a distance of 20 ft or less. Incomparison, existing gating terminals have an end offset of 4 fttypically effected over a distance of 37 ft-6 in. (see U.S. Pat. No.4,678,166, Col. 4, lines 50-58), or an effective flare rate of about10:1.

Full-scale crash testing has demonstrated that a 4-ft end offsetdistance is needed to provide sufficient eccentricity during end-onimpacts to allow an unmodified W-beam rail element to buckle at areasonable force level. Crash testing has also shown that a low flarerate of 10:1 is needed in order to successfully contain and redirectvehicles impacting at or downstream of the beginning of thelength-of-need, again, typically selected to be 12 ft-6 in. from the endof the terminal. The high flare rate used with the present HFT is uniquein the art.

With existing systems, there has been difficulty associated withcontaining vehicles impacting at the beginning of the length-of-needwhen the effective flare rate is higher than the typical 10:1. Forexample, an existing terminal design with a higher effective flare rateof 5 ft over 37 ft-6 in., or an effective flare rate of 7.5:1, fails tocontain and redirect heavy passenger vehicles impacting at the beginningof the length-of-need.

With a long, low flare rate and the beginning of length-of-need set at12 ft-6 in. from the end of the terminal, a terminal is flared forapproximately 25 ft within the length-of-need. As a result, thebeginning of length-of-need is offset approximately 21.7 in. from thetangent portion of the standard section of the guardrail barrier. Incomparison, there is no offset at the beginning of length-of-need forthe HFT terminal of the present invention. FIG. 1A illustrates theschematic layout for a prior art BCT terminal (a traditional flareterminal), and FIG. 1B shows the present inventive HFT terminal.

Offsetting the beginning of the length-of-need behind the tangentportion of the guardrail, as is the design of prior art systems, greatlyaggravates the severity of length-of-need impacts and reduces thecapacity of these non-energy absorbing terminals. It should be notedthat W-beam guardrails contain and redirect errant vehicles usingtensile forces developed in the rail element. Since a convex shape maybe urged to a concave shape without any change in guardrail length,little tensile force is developed upon side impacts until the rail is ina concave shape. By the time sufficient tensile forces are developed inthe rail upon impact, the rail has already deflected substantially andthe vehicle is 2 to 3 feet behind the tangent section of the rail. Thisbehavior, sometimes known as the “pop-through effect,” is illustrated inFIGS. 2A and 2B. FIG. 2A illustrates the long, low flare rate and avehicle initially impacting at the beginning of the length-of-need 50.The convex shape of the flare is moved to a concave shape in FIG. 2Bbefore full tensioning is produced in the guardrail. As may be seen, thevehicle is several feet behind the tangent. The offset at the beginningof length-of-need and the generally convex shape of the flared sectionof the rail in existing prior art systems create the pop-through effect,which in turn increases the potential for adverse situations, such asrail pocketing, post snagging, subsequent rail rupture or excessiveoccupant risk measures.

The present HFT system resolves problems in the prior art systems byshortening the flared section. Thus, the beginning of the length-of-needof the HFT system will be at or very near the downstream end of theterminal, where offset distances are very small. By eliminating theprior art approach of using long, low flare rates, the lateral offset ofthe beginning of length-of-need of the HFT system may be kept at or verynear zero and the redirective capacity of the terminal may be maintainedby eliminating or minimizing the pop-through effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top plan view of a low flare rate guardrail system of theprior art.

FIG. 1B shows a top plan view of the high flare rate guardrail system ofthe present invention.

FIG. 2A is a top plan view of an initial vehicle impact on a prior artlow flare rate guardrail system.

FIG. 2B illustrates a top plan view of the system of FIG. 2A afterimpact and at full tensioning of the guardrail.

FIG. 3A shows a top plan view of the high flare terminal of the presentinvention.

FIG. 3B shows a side elevation view of the system of FIG. 3A.

FIG. 4A is a top plan view of the high flare (linear) configuration ofthe present invention.

FIG. 4B shows a top plan view of the high flare (single curve/singleradius) configuration of the present invention.

FIG. 4C shows a top plan view of the high flare (parabolic)configuration of the present invention.

FIG. 5A illustrates a side elevation view of the high flare terminal ofthe present invention with a shortened second breakaway post.

FIG. 5B shows a top plan view of a vehicle initially impacting theterminal of FIG. 5A at the beginning of the length-of-need.

FIG. 5C shows a top plan view of the terminal of FIG. 5A after theW-beam has passed over the shortened post, tensioning the guardrail, andcontaining and redirecting the vehicle.

FIG. 6A is a rear perspective view of an embodiment of the present highflare terminal with a strut extending between the first breakaway postand the second breakaway post.

FIG. 6B is a top, rear perspective view of the terminal of FIG. 6Aviewing in the downstream direction.

FIG. 6C is a top plan view of the terminal of FIG. 6A upon initialimpact of a vehicle with the strut between the first and second posts.

FIG. 6D is a top plan view of the terminal of FIG. 6A after the struthas been pushed backward, breaking the posts and releasing the anchorcable systems.

FIG. 6E shows an end-on impact of a vehicle with the terminal of FIG.6A.

FIG. 6F illustrates first post breaking and initiating the first impactenergy dissipation; and illustrates the strut telescoping (collapsing).

FIG. 6G shows that the collapsed strut has loaded and broken off thesecond post initiating the second impact energy dissipation.

FIG. 7A is a top, rear perspective view of another embodiment of thepresent invention viewing toward the upstream end of the terminal. Thestrut is attached to the first breakaway post and to the anchor cablebracket on the rail element.

FIG. 7B is a detailed perspective view of the side release mechanism ofthe terminal of FIG. 7A.

FIG. 7C is a top plan view of the terminal of FIG. 7A (without the railelement for clarity) upon initial impact by a vehicle. The second anchorcable mechanism is not shown.

FIG. 7D is a top plan view of the terminal of FIG. 7C after the initialimpact and the strut pivoting at the first post and separated from therelease mechanism.

FIG. 8A is a top, rear perspective view of another embodiment of thepresent invention. This embodiment shows the weld-plug, side releasemechanism of the present invention.

FIG. 8B is a top plan view of the terminal of FIG. 8A (without the railelement for clarity) upon initial impact by a vehicle.

FIG. 8C is a top plan view of the terminal of FIG. 8B after the initialimpact and the strut pivoting at the plug weld.

FIG. 9A illustrates a top, rear perspective view of another embodimentof the present invention. This embodiment utilizes square tabs and ashear pin side release mechanism.

FIG. 9B is a top plan view of the terminal of FIG. 9A (without showingthe rail element) upon initial impact by a vehicle.

FIG. 9C is a top plan view of the terminal of FIG. 9B after the initialimpact and the strut pivoting and shearing about the shear pin.

FIG. 10A is a top, rear perspective view of another embodiment of thepresent invention. This embodiment utilizes angled plates and a shearpin side releasing mechanism.

FIG. 10B is a bottom, rear perspective view of the embodiment of FIG.10A showing the anchor cable passing through a hole in the bottom of thestrut.

FIG. 10C is a top plan view of the terminal of FIG. 10A (without therail element shown) upon initial impact by a vehicle.

FIG. 10D is a top plan view of the terminal of FIG. 10C after theinitial impact.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 3 illustrates a top plan view of HFT system 10 of the presentinvention showing a standard guardrail portion 12 with posts 13 and 15;a high flare rate end terminal section 14; a nose section 16 with a flatplate or thin gauge W-beam 17 with little bending strength and a sideimpact, cable anchor release mechanism 18 attached to a first breakawayend post 20; a second breakaway post 22 with a standard cable anchormechanism 24; a third breakaway post 26; and a buffered end section 28with shield 19 which shields the front edge of the W-beam rail so thatthe vehicle will not spear the W-beam when impacted between posts 20 and22. FIG. 3 also illustrates the beginning of length of need point 50 andthe tangent line 51 for measuring the end offset distances.

The high flare rate end terminal section 14 has a flare rate of 5:1wherein the end offset is 4 feet or more over a distance D of 20 feet orless to the downstream end of the end terminal 14. FIGS. 4A-4Cillustrate that the flare configuration may vary. FIG. 4A shows a linear(straight line) flare 40 a configuration. FIG. 4B illustrates a singlecurve (single radius) flare 40 b configuration. FIG. 4C shows aparabolic (decreasing radius toward the nose of the terminal) flare 40 cconfiguration.

Turning again to FIG. 3, the nose section 16 is attached to a firstbreakaway end post 20 and has an arcuate metal impact head 21 whichwraps around the post 20. Attached at the front side of the arcuateimpact head, plate 17 extends from head 21 downstream to the W-beam 24at buffer shield 19. Plate 17 may be a flat plate or a thin gauge W-beamsection. Since plate 17 carries no tension load, has little bendingstrength, and merely spans the gap or spaces from the arcuate head 21 tothe buffer shield 19, the nose section 16 of the present inventiondiffers from other flat plate designs which shield the end of the railelement and distribute the impact load along the guardrail. These priorart flat plate designs include rounded and buffered W-beam or Thrie-beamend sections, the CAT crash cushion, and the design of U.S. Pat. No.5,765,811. The latter patent discloses that “the end rail is formed by aflat plate maintained in tension along with the standard W-beamguardrail. The flat end rail possesses redirective capabilities whenstruck from the side by a vehicle and does so without distracting fromthe performance of the standard guardrail system with which it may beused.” (Column 1, line 66—Column 2, line 4.) The flat plate 17 of thepresent invention is not intended to dissipate any appreciable energyupon side impact. It allows the impacting vehicle to pass through thebarrier.

Also illustrated in FIG. 3 is the placement of two separate anchormechanisms 18 and 24. The use of a first, side-releasing anchor cablemechanism 18 in cooperation with a second standard anchor cable releasemechanism 24 allows the present invention to utilize a high flare rate(defined as 4 feet or more end offset effected over a distance of 20feet or less) and still ensure that an impacting vehicle will gatethrough the barrier for side impacts before the beginning oflength-of-need. As should be understood from the disclosure herein thatthe present invention allows for tension in the end terminal to bereleased without the need to first break off the first breakaway post inthe terminal.

Side impact cable anchor release mechanism 18 includes an anchor bracket29 fabricated from a bent plate (see FIG. 6A) attached to the W-beamrail 23 with six standard splice bolts 31. Cable 27 is attached at afirst end 27 a to the first breakaway post 20 and at a second end 27 bto the anchor bracket 29 through a variety of alternative side releasemechanisms. The alternative embodiment release structures are disclosedbelow.

One of the purposes of the first anchor mechanism is to assure that thecable anchored to the first post 20 releases for side impacts near theupstream end of the terminal 14 allowing the impacting vehicle to gatethrough the barrier.

The second post 22 is also a breakaway post with a second cable anchorsystem 24 and a standard cable bracket 25 attached to the W-beam 23. Astandard bracket releases the cable tension upon breaking of the post 22and is not intended to release upon side impact as with first anchormechanism 18.

FIG. 5 illustrates that second post 22 may be a shortened post 22 a. Thetop of the post 22 a is disposed below the bottom edge of the W-beam 23.Thus, the beam 23 is not attached to or resting against the post. It isfree to move as the beam 23 is contacted or loaded. For side impacts ator downstream of the beginning-of-need 50 (post 26), the rail element 23will be tensioned earlier in the process since the rail element 23 isnot constrained by post 22 a.

It should be noted that buffer shield 19 is intended to protect thefront edge of the W-beam rail element 23 when there is an impact betweenposts 20 and 22 a, so as to prevent the vehicle from “spearing” on theW-beam 23 and to improve the gate through of the vehicle in advance(upstream) of the beginning of need 50.

As previously indicated, several embodiments of a side impact releasingstructure may be utilized to ensure that upon side impacts near the endof the terminal, the anchor cable 27 is released allowing for gatethrough of the vehicle. FIGS. 6A-6G illustrate a first embodiment.

FIGS. 6A and 6B show an upper strut 60 connecting posts 20 and 22 whichfacilitates the fracture of these posts during impacts on the end of theterminal and upstream of the beginning of the length-of-need. The strut60 is designed with an inner telescoping tube 61 attached to post 20which slides inside an outer tube 63 attached to post 22. The nosesection 16 and the buffer shield 19 are not shown for clarity.

For side impacts between posts 20 and 22 as shown in FIGS. 6C and 6D(the rail elements are not shown for clarity), the vehicle 100 wouldimpact the strut 60 and push the strut backward. As the strut is pushedbackward, it loads and fractures posts 20 and 22 at the base, thusallowing the vehicle 100 to gate through the terminal. In such a case, astandard anchor cable mechanism may be used because tension is releasedwhen both posts fracture.

For end-on impacts as shown in FIGS. 6E-6G, the vehicle would firstimpact and fracture post 20, releasing the cable anchor 18A at post 20.As the vehicle proceeds forward, the inner tube 61 slides inside theouter tube 63, without loading post 22. When post 20 reaches the end ofthe outer tube 63 (FIG. 6G), post 22 would be loaded and fractured, thusreleasing the cable anchor 24 at post 22. The sliding mechanism allowspost 20 to fracture first before post 22 in order to produce twodistinctly separate impacts and reduce the maximum force applied to thevehicle.

FIGS. 7A and 7B show schematic diagrams of another release mechanism andits major components. A special anchor bracket 29 fabricated from a bentplate is attached to the W-beam rail element 23 with standard splicebolts 31. Two triangular plates 54 and 55 are welded to the top of thebent plate to provide a flat surface for the bearing plate (not shown,see FIG. 8A) of the anchor cable 27 to rest against. The anchor cable 27is held in place with a retainer/shear pin 57. The retainer/shear pin 57holds the strut 60 a to the bracket 29 in case tension on the cable isrelaxed for whatever reason. The cable 27 then passes through thedownstream end of strut 60 a and comes out through a hole at the bottomof the strut for attachment to the end post 20. Strut 60 a is attachedat the upstream end to breakaway post 20. It is not connected directlyto breakaway post 22. The strut 60 a is designed with a slider mechanismsimilar to that for the strut between posts 20 and 22, as describedpreviously. An inner tube 61 is attached to post 20, which slides insidean outer tube 63.

For side impacts between posts 20 and 22 as shown in FIGS. 7C and 7D,the vehicle would impact the strut 60 a and push it back, rotating aboutpost 20. As the strut 60 a is pushed back, the retainer/shear pin 57will be sheared, thus releasing the cable anchor 18A and allowing thevehicle 100 to gate through the terminal.

For end-on impacts, the vehicle 100 would first impact and then fracturepost 20, thus releasing the cable anchor 27 at post 20. As the vehicle100 proceeds forward, the inner tube 61 would slide inside the outertube 63, without loading post 22. The sliding mechanism ensures that thestrut 60 a will not interfere with the fracture of post 20 and therelease of the cable anchor 27. When the vehicle reaches the end of theouter tube 63, it will push the strut 60 a into the post 22 and place aload on the post 22 until it fractures and releases cable anchor 24.

FIG. 8A shows a schematic diagram of a plug weld anchor releasemechanism 18B and its major components. A special anchor bracket 29fabricated from a bent plate is attached to the W-beam rail 23 elementwith six standard splice bolts 31. Two square tabs 70 (only one is shownin FIG. 8A) having a hole for setting a weld plug are welded to the topof the bent plate bracket 29 and a strut 72 is in turn attached to thesetabs with plug welds 74. the strut 72 is a unitary, hollow tubularmember which allows the cable 27 to pass through. The anchor cable 27 isbolted to the downstream end of the strut with a bearing plate 75. Theanchor cable 27 then passes through the downstream end of the strut andcomes out through a hole (not shown) at the bottom of the strut forattachment to the end post.

For side impacts between posts 20 and 22 as shown in FIGS. 8B and 8C,the vehicle 100 would impact the strut 72 and push it back. As the strutis pushed back, it rotates about the plug welds 74 and loads the weldmaterial in torsion. The torsional shear stresses eventually fail theplug welds 70, thus releasing the cable anchor 27 and allowing thevehicle 100 to gate through the terminal.

For end-on impacts, the vehicle would first impact and fracture post 20,releasing the cable anchor 27 post 20. The vehicle would then contactthe end of the strut 72 and push the strut 72 into post 22 until thepost fractures and releases the cable anchor 24 at post 22.

FIG. 9A shows a schematic diagram of a plate/shear pin anchor releasemechanism 18C and its major components. A special anchor bracket 29fabricated from a bent plate is attached to the W-beam rail 23 elementwith standard splice bolts. The strut is attached to the anchor bracket29 via a sliding locking mechanism. Two square tabs 80 (only one is seenin FIG. 9A) are welded to the top of the bent plate bracket 29. Twoseparate square tabs 81 are welded to the top and bottom of strut 72.When the cable is in tension, tabs 80 and 81 are urged together and holdthe strut in place. Shear bolt 73 holds the strut 72 to the bracket 29in case tension on the cable is relaxed for whatever reason. The anchorcable 27 is bolted to the downstream end of the strut with a bearingplate 75. The anchor cable then passes through the downstream end of thestrut and comes out through a hole at the bottom of the strut forattachment to the end post.

For side impacts between posts 20 and 22 as shown in FIGS. 9B and 9C,the vehicle 100 would impact the strut 72 and push it back. As the strut72 is pushed back, it rotates about the cable anchor end 79 andeventually fractures the shear bolt 73, allowing tabs 80 and 81 todisengage, thus releasing the cable anchor 27 and allowing the vehicle100 to gate through the terminal.

For end-on impacts, the vehicle 100 would first impact and fracture post20, releasing the cable anchor 27 at post 20. The vehicle 100 would thencontact the end of the strut 72 and push strut 72 into post 22 until thepost 22 fractures and releases the cable anchor 24 at post 22.

FIGS. 10A and 10B show schematic diagrams of an angled plate anchorrelease mechanism and its major components. A special anchor bracket 29fabricated from a bent plate is attached to the W-beam rail 23 elementwith six standard splice bolts 31. A strut 72 is attached to the anchorbracket 29 via four angled plates 76, two on each side. The angledplates 76 are welded to the top of the bent plate bracket 29 on one endand attached to the strut by a shear bolt 77 through the upstreamplates. Welded to the sides of the strut are cooperating angle plates 78which engage with angled plates 76. The positions of the angled plateson the bracket and the strut match so that the strut 72 is held in placewhen tension is applied to the cable (see FIG. 10A). The bolt 77 holdsthe strut 72 to the bracket in case tension on the cable 27 is relaxedfor whatever reason. The anchor cable 27 is bolted to the downstream endof the strut with a bearing plate. The anchor cable 27 then passesthrough the downstream end of the strut and comes out through a hole 80at the bottom of the strut for attachment to the end post.

For side impacts between posts 20 and 22 as shown in FIGS. 10C and 10D,the vehicle 100 would impact the strut 72 and push it back. As the strutis pushed back, it rotates about the cable anchor end 79 and eventuallybreaks the shear bolt 77 and the angled plates 76 and 78 slide apart anddisengage, thus releasing the cable anchor 27 and allowing the vehicle100 to gate through the terminal.

For end-on impacts, the vehicle 100 would first impact and fracture post20, releasing the cable anchor 27 at post 20. The vehicle 100 would thencontact the end of the strut 72 and push the strut into post 22 untilthe post fractures and releases the cable anchor 24 at post 22.

As should be understood from the disclosure and drawings, the HFTterminal of the present invention has several advantages over otherexisting non-energy absorbing or gating terminals:

-   -   1. A shorter and thus less expensive terminal.    -   2. Only two or three posts to position for field installation        instead of the typical six posts for existing terminals.    -   3. There effectively is no length-of-need section in the        terminal, i.e., the beginning of length-of-need is at the end of        terminal.    -   4. Higher anchorage capacity since there are two anchors instead        of one for existing terminals. In addition, the anchor at post        22 is more in line with the tangent section of the guardrail and        thus less lateral offset and pop through effect.

While the systems and methods of this invention have described in termsof preferred embodiments, it will be apparent to those of skill in theart that variations may be applied to the systems, methods, and in thesteps or in the sequence of steps of the method described herein withoutdeparting from the concept, spirit and scope of the invention. Morespecifically, it will be apparent that certain materials that are bothfunctionally and mechanically related might be substituted for thematerials described herein while the same or similar results would beachieved. All such similar substitutes and modifications to thoseskilled in the art are deemed to be within the spirit, scope and conceptof the invention as defined by the appended claims.

1. A guardrail system comprising a standard length of need section and aterminal end, the terminal end having a high effective flare rate of atleast 5:1.
 2. The system of claim 1 further comprising two independentbreakaway end posts and cooperating cable anchor mechanisms.
 3. Thesystem of claim 1 further comprising a side impact releasing mechanismfor disengagement of an anchor cable from a rail element of saidterminal end to facilitate breakaway of end posts in side impacts nearthe terminal end.
 4. The system of claim 3, wherein the side releasingmechanism is selected from the group consisting of a strut connecting afirst and a second breakaway post, a strut anchor release affixed at afirst end to a first breakaway post and at a second end to the railelement, a strut with a plug weld anchor release, a strut with a shearbolt anchor release, and a strut with an angled plate anchor release. 5.The system of claim 2 further comprising a shortened post between afirst breakaway post and a third breakaway post to allow earlierdevelopment of tensile force in a guardrail of the system and tominimize potential for vehicular snagging.